This invention relates to portable acoustical terminals of the type employed in conjunction with a telephone handset.
Portable terminals are known which are designed for use with telephone handsets for the purpose of sending and receiving information in the form of digital pulses along the transmission lines of the telephone system. Such devices, of which the disclosure in U.S. Pat. No. 3,976,840 issued Aug. 24, 1976 is representative, incorporates a manually operable keyboard for enabling manual selection of information to be transmitted to a site remote from the portable terminal, a pair of acoustic couplers for enabling the device to be acoustically coupled to the transmitter and receiver portions of a convention telephone handset with efficient acoustical isolation from the ambient noise, and electrical circuitry for converting keyboard generated electrical signals into acoustical signals within the telephone system bandwidth for transmission to a remote site and for converting acoustical signals generated by the telephone receiver in response to receipt of electrical signals from the remote site into electrical signals for operating a visible display. While the device disclosed in the abovereferenced U.S. Pat. No. 3,976,840 is specifically designed for use in transmitting and receiving securities quotation and transaction execution requests, many other potential uses exist for a portable terminal incorporating the elements noted above. Examples of such potential uses are a portable credit card verification terminal for enabling small retailers to participate in a computer based credit card veritification system, a field support terminal for sales personnel for enabling orders to be placed directly, and for inventory to be queried, via telephone to a centralized computer, a portable telegram terminal for enabling users to send a telegram via computer without the necessity of intervention by a human operator, a retail order entry terminal for customer use with mail order catalogs, and similar applications.
Common to all such uses of portable terminals of the above type, regardless of the field of application, is the requirement that the device be mechanically stable when physically coupled to the telephone handset so as to render the keyboard and display readily useable by the operator. Efforts to date to design a truly portable terminal with the required mechanical stability when coupled to the telephone handset have not met with wide success.